The invention pertains to methods of forming microstructure devices, such as, for example, methods of forming microelectromechanical systems (MEMS).
There are numerous applications developed, and being developed, for microstructures, such as, for example, microelectromechanical systems (MEMS). The microstructures are commonly fabricated from semiconductive materials, such as, for example, silicon. Frequently, a microstructure will include a pair of components which are spaced from one another, and which move relative to one another during operation of the microstructure. Ideally, the components can be repeatedly moved together and apart. However, a problem that can occur in forming and using microstructures is that semiconductive materials formed into MEMS can irreversibly adhere to one another as they are moved toward one another or during the fabrication process. Such problem can be manifested as an inability to release the materials, and the release-related problem is typically referred to in the art as xe2x80x9cstictionxe2x80x9d.
An exemplary prior art fabrication process for forming a microstructure device is described with reference to FIGS. 1-3. Referring initially to FIG. 1, a portion of a prior art semiconductive assembly 10 is shown in fragmentary view at a step occurring during a micromachining process. Assembly 10 comprises a first semiconductive material 12, a sacrificial layer 14 over material 12, and a second semiconductive material 16 over sacrificial layer 14. Semiconductive material 12 can comprise, for example, a single-crystal silicon wafer, or can comprise silicon in a polycrystalline or amorphous form. Sacrificial layer 14 can comprise, for example, silicon dioxide or organic films; and second semiconductive material 16 can comprise, for example, polycrystalline or amorphous silicon. Material 12 can be referred to as a semiconductive material substrate, or alternatively a combination of materials 12 and 14 can be referred to as a semiconductive material substrate. To aid in interpretation of this disclosure and the claims that follow, the terms xe2x80x9csemiconductive substratexe2x80x9d and xe2x80x9csemiconductor substratexe2x80x9d are defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term xe2x80x9csubstratexe2x80x9d refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
It is to be understood that the above described materials 12, 14 and 16 are exemplary materials, and that other materials can be utilized. For instance, material 16 will sometimes comprise silicon nitride, and sacrificial material 14 will sometimes be silicon.
Referring next to FIG. 2, sacrificial layer 14 (FIG. 1) is removed to leave a first gap 20 between a portion of first semiconductive material 12 and second semiconductive material 16, and a second gap 22 between another portion of first semiconductive material 12 and second semiconductive material 16. Second semiconductive material 16 defines a beam supported by first semiconductive material 12. If sacrificial material 14 comprises silicon dioxide, such can be removed utilizing a hydrofluoric acid etch.
Referring next to FIG. 3, a stiction problem is illustrated. Specifically, a portion of second semiconductive material 16 has moved relative to first semiconductive material 12 and is non-releasably adhered to the first semiconductive material. The movement of second semiconductive material 16 relative to first semiconductive material 12 can occur either during operation of a device comprising assembly 10, or during removal of sacrificial layer 14. If the stiction occurs concomitantly with removal of sacrificial layer 14 (FIG. 1) it is referred to as xe2x80x9crelease-related stictionxe2x80x9d, and if it occurs after removal of sacrificial layer 14, (for example, during utilization or shipping of a microstructure comprising assembly 10), it is referred to as xe2x80x9cin-use stiction.xe2x80x9d
It has been recognized that one way to alleviate the release-related stiction is to use supercritical CO2 drying. Also, it has been recognized that one way to alleviate in-use stiction is to form a self-assembled monolayer (SAM) coating across semiconductive material surfaces to alleviate binding of the surfaces to one another. An exemplary SAM coating can be formed by exposing a semiconductive material surface to an alkyltrichlorosilane (RSiCl3), such as, for example, octadecyltrichlorosilane [CH3(CH2)17SiCl3; OTS] or 1H, 1H,2H,2H-perfluorodecyltrichlorosilane [CF3(CF2)7(CH2)2SiCl3; FDTS]. Alternatively, an exemplary SAM coating can be formed by exposing a semiconductive material surface to a dialkyldichlorosilane (R2SiCl2).
For purposes of interpreting this disclosure and the claims that follow, semiconductive materials 16 and 12 are referred to as being moved relative to one another if either of components 12 and 16 comprises a portion which moves relative to a portion of the other of the components. In particular applications, both of components 12 and 16 can be moved when the components are moved relative to one another.
In one aspect, the invention encompasses a method of forming a microstructure device. A substrate is provided within a reaction chamber. The substrate has a first surface spaced from a second surface, and is ultimately to be incorporated into the microstructure device. The first and second surfaces are ultimately to be movable relative to one another in the microstructure device. Alkylsilane-containing molecules are introduced into the reaction chamber in a vapor phase, and at least one of the first and second surfaces is exposed to the alkylsilane-containing molecules to form a coating on the at least one of the first and second surfaces.
In another aspect, the invention encompasses another method of forming a microstructure device. A substrate is provided which has a first semiconductive material surface separated from a second semiconductive material surface by a gap. At least one of the first and second semiconductive material surfaces is exposed to OH radicals. After the exposure to the OH radicals, the at least one of the first and second semiconductive material surfaces is exposed to vapor-phase alkylsilane-containing molecules to form a coating over the at least one of the first and second semiconductive material surfaces.
In yet another aspect, the invention encompasses another method of forming a microstructure device. A substrate is provided which has a first semiconductive material, a second semiconductive material, and a sacrificial material between the first and second semiconductive materials. The substrate is exposed to vapor-phase etchant to remove at least some of the sacrificial material from between the first and second semiconductive materials, and subsequently at least one of the first and second semiconductive materials is exposed to vapor-phase alkylsilane-containing molecules to form a coating over the at least one of the first and second semiconductive materials. The method can be utilized to solve both release-related and in-use stiction problems.